This invention relates to dry etching of aluminum and aluminum-rich alloys.
In the fabrication of semiconductor devices, the advantages of dry etching, such as plasma and reactive sputter etching, in permitting better control of the etching features is becoming increasingly recognized and dry etching is now well established, particularly in the preparation of semiconductive chips involving fine detail, such as is involved in large capacity memory chips.
In semiconductor technology, a favored metal for use in providing interconnections is aluminum either in pure form or more commonly alloyed with relatively small amounts of additives, such as copper or silicon, which will still be referred to hereinafter as aluminum.
Accordingly, there is a need in semiconductor technology for a dry etching process for patterning such aluminum layers.
Various techniques have been proposed hitherto. Typically these involve forming a plasma of a gas which, after ionization, selectively reacts with aluminum to etch it preferentially, and in which the reactive energetic ions impinge on the aluminum workpiece with sufficient directionality that the aluminum is etched anisotropically. This is to provide substantially vertical edges to the etched pattern and to reduce the waste of lateral area of the semiconductive chip.
It is now generally recognized that the chlorine ion is especially effective for etching aluminum because of the low vapor pressure and hence volatility of aluminum chloride which is readily formed by its interaction with aluminum. In the past the chlorine ion typically has been derived by the inclusion of chlorine gas either alone or in combination with boron trichloride or carbon tetrachloride gas. The combinations have been found preferable where the aluminum layer had developed a native oxide film which had to be bared to reach the aluminum metal. One problem with such systems has been the strong tendency with the use of such gas systems to form polymer deposits on the equipment which interferes with the normal operation. Such tendency often is the result of moisture in the apparatus.